1. Field of the Invention
The present invention relates to an external type liquid crystal display including a liquid crystal cell having a pair of opposing transparent substrates with a liquid crystal layer held therebetween, and a reflector provided on an outer surface of the liquid crystal cell. The invention more particularly relates to a liquid crystal display having improved visibility by providing the liquid crystal cell with a light scattering characteristic.
2. Description of the Related Art
Liquid crystal displays are generally divided into semi-transmissive or transmissive type displays having a backlight and reflective type displays. The reflective type liquid crystal display utilizes only external light such as sunlight and illumination for display and does not use a backlight. This type of display is widely used for mobile information terminals that should be thin and lightweight, and operate with low power consumption. The reflective type liquid crystal display includes a reflector that reflects incoming light from the display surface side for display. Some reflectors have a mirror surface and others have an irregular surface. The reflector having, an irregular surface is more suitable for obtaining a wider viewing angle than the reflector with a mirror surface.
FIG. 4 is a schematic sectional view of a conventional reflective type liquid crystal display including a reflector with an irregular surface. The conventional liquid crystal display 200 includes a liquid crystal cell 220, and a front light 210 provided in front of the liquid crystal cell 220 (in the upper part of FIG. 4).
The conventional front light 210 includes a light guide plate 212, and a light source 213 of a cold cathode tube provided at the side end face 212a of the light guide plate 212. The light guide plate 212 has an emission surface 212b as a lower surface (the surface on the side of the liquid crystal cell 220), from which light is emitted. The surface on the opposite, side to the emission surface 212b (the upper surface of the light guide plate 212) is a prism surface 212c that can change the optical path of light propagating through the light guide plate 212 toward the emission surface 212b. 
The liquid crystal cell 220 has first and second opposing substrates 221 and 222 joined to each other by a seal member 224 and having a liquid crystal layer 223 therebetween. There are display circuits 226 and 227 on the first and second substrates 221 and 222 on the side of the liquid crystal layer 223 (at the inner side). A reflector 230 is provided on the side of the first substrate 221 opposite to the liquid crystal layer 223 (at the outer side) through an adhesive layer 231. The reflector 230 includes a reflector substrate 228 having one irregular surface, and a reflection layer 229 formed on the irregular surface of the reflector substrate 228. The reflection layer 229 is located on the side of the first substrate 221.
In the liquid crystal display 200 having the above structure, when the front light 210 is turned on, light emitted from the light source 213 is propagated in the light guide plate 212 and emitted from the emission surface 212b. The light emitted from the emission surface 212b is let into the liquid crystal cell 220 as the illumination light, sequentially passed through the second substrate 222, the display circuit 226, the liquid crystal layer 223, the display circuit 227, the first substrate 221, and the adhesive layer 231 and reflected by the reflection layer 229. The reflected light is returned to the outer side of the liquid crystal cell 220 (the side of the front light 210), and reaches the viewer through the emission surface 212b and the prism surface 212c of the front light 210. In this way, the displayed content at the liquid crystal cell 220 is viewed by the viewer.
When sunlight is used for display rather than turning on the front light 210, sunlight comes into the liquid crystal cell 220 through the prism surface 212c and the emission surface 212b of the front light 210, and light reflected by the reflection layer 229 is viewed by the viewer similarly to the above described case.
However, the on going development and designing of the reflective type liquid crystal displays including the reflector with the irregular reflection surface aims at forming fine irregularities (raise and recessed portions) on the reflection surface to adjust the angle of the reflected light and controlling the irregular geometry to control even the directivity of the reflected light. The fine irregularities on the reflection surface surely improve the controllability of the reflected light, but there is a problem that a spectrum is more likely to occur under intense sunlight, which could cause a rainbow-like pattern (hereinafter simply as xe2x80x9crainbowxe2x80x9d) to be observed on the display screen, in other words, the visibility is lowered.
The present invention is directed to a solution to the above problem, and a liquid crystal display including a reflector having an irregular surface that can prevent a rainbow from appearing on the screen is provided.
In order to solve the above problem, the liquid crystal display according to the invention includes a pair of opposing transparent substrates having a liquid crystal layer held therebetween. An outer surface of one of the transparent substrates serves as a light scattering surface having a light scattering characteristic. A reflector having an irregular reflection surface is provided on the light scattering surface so that the reflection surface is on the side of the light scattering surface.
The liquid crystal display according to the invention includes the light scattering surface between the reflection surface and the liquid crystal layer, and therefore light reflected by the reflection surface of the reflector is scattered as it passes through the light scattering surface, despite a spectrum caused at the irregularities at the reflection surface. Therefore, the rainbow is prevented from being generated at the display screen.
According to the invention, the light scattering surface preferably has irregularities.
In this manner, the outer surface of one of the transparent substrates on the side (light scattering surface) having the reflector is provided with irregularities, so that the surface may have a preferable light scattering characteristic.
According to the invention, the haze of the light, scattering surface is preferably in the range from 15% to 30%.
As will be described, the haze is an index of the degree of light scattering. When the outer surface (light scattering surface) of the above-mentioned one transparent substrate has too small a light scattering characteristic, there is not a sufficient rainbow elimination effect at the display screen. Meanwhile, when the light scattering characteristic is too large, the display characteristic at the screen is significantly lowered. When the haze at the outer surface (light scattering surface) of the above mentioned one transparent substrate is in the range from 15% to 30%, the display characteristic of the liquid crystal display can be restrained from being lowered, while the rainbow at the display screen can be prevented.
According to the invention, the reflector is provided on the light scattering surface through the adhesive layer and the difference between the refractive index of one transparent substrate having the light scattering surface and the refractive index of the adhesive layer is preferably at least 0.01.
In this way, the refractive indexes of the light scattering surface and the adhesive layer can be different, so that light reflected by the reflection surface of the reflector can effectively be scattered at the light scattering surface, and the rainbow can be prevented from being generated.
The thickness of one transparent substrate having the light scattering surface is preferably smaller than the thickness of the other transparent substrate.
The illumination light passed through the liquid crystal layer near the reflector is let into the above mentioned one transparent substrate, passed the substrate and then reflected by the reflector. The reflected light is passed once again through the above described transparent substrate and then passed through the liquid crystal layer.
When the above mentioned one transparent substrate provided near the reflector is made thinner, the display can become even thinner and lighter, and the transmission loss as the light passes through the transparent substrate can be reduced.
When the above mentioned one transparent substrate is made thinner, the shift between the position where the light passes before the reflection and the position where the light reflected by the reflector passes through can be smaller at the interface between the liquid crystal layer and the transparent substrate. Therefore, clearer display can be provided. When in particular a color filter is provided on the transparent substrate that is thin, the shift between the position of the color filter where the light passes before the reflection, and the position of the color filter where the illumination light reflected by the reflector passes can be smaller. Therefore, color shift and parallax can be reduced and high definition color display can be carried out.